1. Field of the Invention
The present invention relates to wellbore completion. More particularly, the invention relates to an apparatus and method for expanding a tubular body. More particularly still, the apparatus relates to an expander tool for expanding a section of tubulars within a wellbore.
2. Description of the Related Art
Hydrocarbon and other wells are completed by forming a borehole in the earth and then lining the borehole with steel pipe or casing to form a wellbore. After a section of wellbore is formed by drilling, a string of casing is lowered into the wellbore and temporarily hung therein from the surface of the well. Using apparatus known in the art, the casing is cemented into the wellbore by circulating cement into the annular area defined between the outer wall of the casing and the borehole. The combination of cement and casing strengthens the wellbore and facilitates the isolation of certain areas of the formation behind the casing for the production of hydrocarbons.
It is common to employ more than one string of casing in a wellbore. In this respect, a first string of casing is set in the wellbore when the well is drilled to a first designated depth. The first string of casing is hung from the surface, and then cement is circulated into the annulus behind the casing. The well is then drilled to a second designated depth, and a second string of casing, or liner, is run into the well. The second string is set at a depth such that the upper portion of the second string of casing overlaps the lower portion of the first string of casing. The second liner string is then fixed or xe2x80x9chungxe2x80x9d off of the existing casing by the use of slips which utilize slip members and cones to wedgingly fix the new string of liner in the wellbore. The second casing string is then cemented. This process is typically repeated with additional casing strings until the well has been drilled to total depth. In this manner, wells are typically formed with two or more strings of casing of an ever decreasing diameter.
Apparatus and methods are emerging that permit tubular bodies to be expanded within a wellbore. The apparatus typically includes an expander tool that is run into the wellbore on a working string. The expander tool includes radially expandable members, or xe2x80x9cexpansion assemblies,xe2x80x9d which are urged radially outward from a body of the expander tool, either in response to mechanical forces, or in response to fluid injected into the working string. The expansion assemblies are expanded into contact with a surrounding tubular body. Outward force applied by the expansion assemblies cause the surrounding tubular to be expanded. Rotation of the expander tool, in turn, creates a radial expansion of the tubular.
Multiple uses for expandable tubulars are being discovered. For example, an intermediate string of casing can be hung off of a string of surface casing by expanding an upper portion of the intermediate casing string into frictional contact with the lower portion of surface casing therearound. Additionally, a sand screen can be expanded into contact with a surrounding formation in order to enlarge the inner diameter of the wellbore. Additional applications for the expansion of downhole tubulars exist.
An exemplary embodiment of an expander tool previously known as of the filing of this continuation-in-part application is shown in FIG. 1. FIG. 1 is an exploded view of an exemplary expander tool 100. FIG. 2 presents the same expander tool 100 in cross-section, with the view taken across line 2xe2x80x942 of FIG. 1.
The expander tool 100 has a body 102 which is hollow and generally tubular. The central body 102 has a plurality of recesses 114 to hold a respective expansion assembly 110. Each of the recesses 114 has parallel sides and holds a respective piston 120. The pistons 120 are radially slidable, one piston 120 being slidably sealed within each recess 114. The back side of each piston 120 is exposed to the pressure of fluid within a hollow bore 115 of the expander tool 100. In this manner, pressurized fluid provided from the surface of the well can actuate the pistons 120 and cause them to extend outwardly.
Disposed within each piston 120 is a roller 116. In one embodiment of the expander tool 100, the rollers 116 are near cylindrical and slightly barreled. Such a roller 116 is sometimes referred to as a xe2x80x9cparallelxe2x80x9d roller because it includes a side portion that resides parallel to the surrounding tubular to be expanded. Each of the rollers 116 is supported by a shaft 118 at each end of the respective roller 116 for rotation about a respective axis. The rollers 116 are generally parallel to the longitudinal axis of the tool 100. In the arrangement of FIG. 1, the plurality of rollers 116 are radially offset at mutual 120-degree circumferential separations around the central body 102. In the arrangement shown in FIG. 1, two offset rows of rollers 116 are shown. However, only one row, or more than two rows of roller 116, may be incorporated into the body 102.
As sufficient pressure is generated on the piston surface behind the expansion assembly 110, the tubular being acted upon (not shown) by the expander tool 110 is expanded past its point of elastic deformation. In this manner, the inner and outer diameter of the tubular is increased within the wellbore. By rotating the expander tool 100 in the wellbore and/or moving the expander tool 100 axially in the wellbore with the expansion assemblies 110 actuated, a tubular can be expanded into plastic deformation along a predetermined length. Where the expander tool 100 is translated within the wellbore, the shaft 118 serves as a thrust bearing.
One disadvantage to known expander tools, such as the hydraulic tool 100 shown in FIGS. 1-2, is the inherently restricted size of the hollow bore 115. In this respect, the dimension of the bore 115 is limited by the size of the expansion assemblies 110 radially disposed around the body 102 of the tool 100. The constricted bore 115 size, in turn, imposes a limitation on the volume of fluid that can be injected through the working string at any given pressure. Further, the dimensions of the bore 115 in known expander tools place a limit on the types of other tools which can be dropped through the expander tool 100. Examples of such tools include balls, darts, retrieving instruments, fishing tools, bridge plugs and other common wellbore completion tools.
In addition, the tubulars being expanded within a wellbore generally define a thick-walled, high-strength steel body. To effectively expand such tubulars, a large cross-sectional geometry is required for the roller body 116. This further limits the inner bore diameter, thereby preventing adequate flow rates, and minimizing the space available to run equipment through the inner bore 115. Also, the stresses required to expand the material are very high; hence, reducing the roller body size to accommodate a larger inner bore diameter would mechanically weaken the roller mechanism, thereby compromising the functionality of the expansion assembly.
Therefore, a need exists for an expander tool which provides for a larger configuration for the hollow bore 115 therein. Further, a need exists for an expander tool which reduces the size of the expansion assemblies 110 around the tool 100 so as to allow for a greater bore 115 size. Further, a need exists for an expander tool having expansion assemblies which do not rely upon rollers 116 rotating about a shaft 118 at a spaced apart distance from the piston member 120.
The present invention provides an apparatus for expanding a surrounding tubular body. More specifically, an improved expansion assembly for a radially rotated expander tool is disclosed. In addition, a method for expanding a tubular body, such as a string of casing within a hydrocarbon wellbore, is provided, which employs the improved expansion assembly of the present invention.
The expansion assembly first comprises a piston. The piston is preferably an elongated wafer-shaped body which is sealingly disposed within an appropriately configured recess of an expander tool. The piston has a top surface and a bottom surface. The top surface includes a bearing cavity for receiving a roller. In the expansion assembly of the present invention, the roller does not rotate about a shaft; rather, the roller is permitted to rotate within the bearing cavity of the piston during an expansion operation.
The bearing cavity of the piston is configured to retain the roller while it is operated within a wellbore. In one aspect, the expansion assembly provides a headrest for supporting the upper end of the roller. The piston further provides a shoe for receiving the lower end of the roller. The lower end of the roller is gravitationally retained within the shoe during operation.
In another aspect, the expansion assembly of the present invention provides for a cap piece. The cap piece is fitted over the headrest to further secure the headrest onto the piston member. In one aspect, the headrest further helps to secure the roller within the bearing cavity during operation.
The bottom surface of the piston is exposed to an outwardly radial force. In one aspect, the force is a hydraulic force generated by wellbore fluids within the bore of the expander tool. In another aspect, the hydraulic pressure is from a dedicated fluid reservoir in fluid communication with the expander tool downhole. Alternatively, a mechanical force may be employed. The piston is moved radially outward from the body of the expander tool but within the recess in response to the radially outward force. Because the roller is held closely to the piston within the bearing cavity, greater space is accommodated for the bore within the expander tool.